Percussion bit



` DEC 12, 1967 v. G. STEWART 3,357,507L

PERCUSSION BIT Filed Oct. 24, 1965 2 Sheets-Sheet l ATTORNEY UnitedStates Patent Otice 3,357,507 Patented Dec. 12, 1967 3,357,507PERCUSSION BIT Vernon G. Stewart, Houston, Tex., assignor to MissionManufacturing Company, Houston, Tex., a corporation of Texas Filed Get.24, 1965, Ser. No. 594,608 Claims. (Ci. 175-410) ABSTRACT 0F THEDISCLOSURE A solid, button-insert-type percussion bit in which two rowsof cutter inserts are provided at or adjacent the periphery inclinedoutwardly at different angles. The outer row of inserts are disposed tomaintain the hole at gauge, and the inner row of these inserts cut onlythe hole bottom. The cutting extremities of the outermost row of insertsare spaced substantially upwardly and outwardly from the extremities ofthe inner inserts to form a shoulder or shelf at the periphery of thehole bottom which facilitates chipping out this part of the hole. Thebit may be provided with a drop center and a row of inwardlyanddownwardly-inclined cutter inserts at the edge thereof to assist inchipping away the center core.

This invention relates to a drill bit. More particularly, this inventionrelates to a bit of the solid, button-inserttype for drilling a borehole into a subterranean formation, as by the rotary-percussion method,wherein the ybit is so constructed as to faciltate drilling of the outerdiameter of the bore hole to maintain the gauge thereof.

The drilling of bore holes by the rotary-percussion method has long beenknown in the art. In such a method, a bit, having one or more cuttingsurfaces at its lower end, while being rotated is subjected to asuccession of vertical impacts from the impactmember of a percussiontool. The rotation of the bit causes the cutting surfaces to index aboutthe bits longitudinal axis between each impact, so that substantiallythe entire bottom surface of the bore hole will be chipped away. Thechips or cuttings are customarily carried to the surface by a flushingfluid, such as air, which is passed down a hollow drill stem, throughpassages in the bit, and thence up the annulus between the drill sternand bore hole wall.

To prevent excessive wear of the bits cutting elements and to improvethe cutting action, these elements are usually made of a hard, tough,wear-resistant material such as tungsten carbide. This material may beembodied in the bit body in the form of button-like inserts.

One problem that the percussion drilling industry has long faced isthat, during drilling, the wear-resistant inserts, which, being locatednearest to the periphery of the bottom surface of the bit, must do agreater proportion of the work and are subjected to greater forces thanthose inserts which are closer to the center of the bits bottom surface,subjecting the outer inserts to rapid wear and to cracking or otherfailure. While it may be postulated that this problem could be solvedmerely by utilizing a greater number of inserts near the outer edge,such a solution is impractical in practice because the amount of bitbody metal surrounding the inserts becomes insufficient to adequatelysupport them. Also, because the percussion tool can only impart a givenamount of energy to the bit with each impact, the amount of energytransmitted through each insert will become insuflicient to causedesirable rock fracture, and will in turn decrease the drilling rate.

It is also important to prevent reduction of the gauge or diameter ofthe bit body during drilling. 1f inserts are not positioned to engagethe wall of the ybore hole, the

wall will contact and wear away the relatively soft metal of theperipheral surface of the body and cause a reduction in the diameter ofthe hole and bit as drilling progresses.

It is, accordingly, an object of the invention to provide a bit adaptedto prevent excessive loading and wear on the portions thereof which cutthe bottom of the bore hole nearest the side wall.

It is a further object of the invention to provide a bit adapted toprevent wear on the peripheral surface of the bit body and having meansfor reducing the loading and wear on the portion of the bit which cutsthe bottom of the bore hole nearest the side wall.

According to the present invention, action of the bit is improved bydisposition of its outermost cutting inserts so as to impact against theupper and inner side surfaces of a shelf or shoulder-like protrusionformed by the same inserts at the intersection of the bottom and theside wall of the bore hole. These outenmost inserts are formed in afirst annular row projecting below the bottom surface, but are spacedinwardly of the side surface, and a second annular row projectingoutwardly beyond the side surface, and with its cutting extremitiesspaced substantially above and outwardly of the cutting extremies of therst row. The mentioned shoulder-like protrusion at the periphery of thehole bottom forms in the cutter free space between these rows.

It has been found that the formation of such a shoulder substantiallyreduces the work which must be performed by the outermost inserts, inthat such a shoulder may be more easily fractured and broken off,especially in friable formations, than if the outermost inserts were toimpact directly upon the bottom of the bore hole.

Other objects and advantages of the invention will further becomeapparent upon consideration of the following detailed description andthe accompanying drawings, in which:

FIGURE 1 is a plan view of the bottom surface of one embodiment of thebit of my invention;

FIGURE 2 is a sectional view of the lower portion of the bit, taken online 2 2 of FIGURE l;

FIGURE 3 is a sectional view of the lower portion of the bit, taken online 3 3 of FIGURE l and with all of the inserts except inserts 7omitted for clarity; and

FIGURE 4 is an enlarged fragmental sectional view taken on line 4 4 ofFIGURE l, with inserts 10 omitted for clarity.

Referring now to the drawings, there is illustrated a preferred form ofone embodiment of the bit of the invention, consisting of a body 1 ofsteel or other suitable material. Body 1 is preferably forged orotherwise formed from a single piece of material.

The upper end of the body is not shown in the drawings, as the structurethereof is entirely conventional and will depend upon the particulartype of rotary-percussion tool to which the bit is to be attached. Theupper end of the body may, for example, be a pin or female box joint,but in the preferred form of the invention it is formed as shown in U.S.Patent No. 3,105,559. As shown and described in that patent, theintegral anvil-bit is slidably but non-rotatably attached to a drillingtool by means of a splined connection, and a hammer in the tool actsupon the upper end of the anvil bit to drive the latter verticallyagainst the bottom of the bore hole by repeated impacts. Such tool alsoprovides for supplying fluid from the interior of the hollow drill stemto a central bore in the bit.

The bit body 1 illustrated in the drawings is of substantially circularhorizontal cross-section about its longitudinal axis and throughout itslength. Below its upper end, the diameter of the body increases instepwise fashion, 'having an intermediate portion 2 and a largerdiameter portion 3 therebelow. The outer peripheral surface 4 of thelower portion 3 may be cylindrical, as shown, or may taper slightlydownwardly and outwardly.

The bottom surface 5 of the bit is, as shown, a generally liat,transverse plane perpendicular to the longitudinal axis of the bit. Thecentral portion of the bottom surface is elevated to form a cylindricalcavity or pocket t 6 (drop center) provided with downwardly-projectingwear-resistant inserts 7 of the type to be hereinafter described. At theintersection of the side wall of pocket 6 and bottom surface 5 is anannular chamfer 8 (FIG. 4), with downwardly and inwardly inclined,wear-resistant inserts 9 circumferentially spaced therearound andprotruding therefrom. Alternatively, pocket 6 may be omitted, ifdesired, and the bit may simply be rprovided with a iiat bottom surfacecontaining inserts arranged in circular rows (similar to inserts 10) orin some other pattern.

In order to chip and cut away the bottom surface of the bore hole, thereare provided intermediately in the bit bottom surface one or more setsof wear-resistant inserts 10. These inserts 10 protrude through surface5 with their longitudinal axes normal thereto and are arranged in acircle concentric about the longitudinal axis of the bit body. Thenumber of circular sets of inserts used will be dependent on the size ofthe inserts used and the bit diameter, but in most cases the insertswill be so arranged that their protruding (free) ends lie in a planeparallel to bottom surface 5.

In the region of the intersection of the bit bottom surface 5 with theouter peripheral surface 4, there are provided viirst and secondconcentric annular chamfers 12 and 13, outer chamfer 12 being taperedupwardly and outwardly to a greater degree than inner surface 13. As ismore clearly shown in FIGURE 4, the rows of circumferentially-spaced,wear-resistant inserts 14, 11 protrude respectively through each ofthese chamfers with their longitudinal axes substantially normal to therespective chamfer. Thus, the longitudinal axis of each insert 14, 11will extend at an acute angle to the longitudinal axis of the bit bodywith the angle of inserts 14 being greater than that of inserts 11. Aswill be hereinafter described, this inclination of inserts 14, 11 is animportant feature of the invention.

It will be observed from FIGURE 4 that the protruding or free ends ofouter inserts 14 do not lie in the same horizontal plane as the freeends of inner inserts 11, but are spaced thereabove by a distance D. Asshown in FIG- URE 4, this spacing causes a shoulder-like shelf orprotrusion S to be formed in the formation substantially at theintersection of the side wall and bottom of the bore hole duringdrilling, likewise an important feature of the invention. Furthermore,the free ends of outer inserts 14 extend beyond the outer peripheralsurface 4 of the bit body to cut the side wall and prevent the same fromcontacting surface4, wearing away surface 4, and reducing the diameterof the bit body.

As used herein, the term wear-resistant insert refers to a discreteinsert made of tungsten carbide or other relatively hard andwear-resistant material, of a hardness considerably greater than that ofthe bit body. The inserts shown in the drawing are generally cylindricalin form and preferably have free or protruding ends of hemisphericalshape, although inserts having free ends of various other shapes may beused, if desired. The inserts are located in the bit body by insertingthem into suitable holes drilled or otherwise formed in the body, andare secured therein by press fitting, brazing, or other means.

The bit shown is provided with a flushing uid passage system consistingof central bore 16 and two pairs of passages 17, 18 leading therefrom todischarge iluid adjacent the lower end of the bit. Passages 17 dischargefluid into central cavity 6 to pick up the cuttings formed therein andcarry them outwardly and upwardly, radial channels 19, 20 and bodyflutes 21, 22 facilitating this movement. Chamfers 12 and 13 alsofacilitate this flow.

In operation, the bit of my invention is rotated at a suitable speed(e.g., 13 to 16 r.p.m.), while being subjected to a succession ofvertical impacts. The rotation causes the bit to index about itslongitudinal axis between successive impacts.

As drilling progresses, inserts 9, 10 will cut or chip off pieces of theformation from the bottom of the bore` hole. If the bit is of thetypehaving a pocket 6, the p0r-` tion of the bore hole bottom adjacentthe pocket will not be immediately attacked and a cylindrical plug orcore of material will risev in the pocket as the bit penetrates, theformation. When the top of this plug is finally contacted by centralinserts 7, it may be relatively easily broken up by their impacts, incooperation with `the action of inclined inserts 9, into relativelylarge pieces, as it is not supported at its sides by any surroundingsubterranean material and consequently presents less resistance than thematerial around this core.

During drilling, inserts 14 and 11 will likewise be impacted against theformation and, because the free ends of inserts 14 are spaced verticallyand radially from inserts 11 and the space between these inserts is freeof cutting elements, the shoulder-like shelf or protrusion S, whosedepth is approximately equal to D, will be formed at the intersection ofthe side wall and bottom of the bore hole. Inserts 14 protrude beyondthe peripheral surface 4 of the bit body to maintain the gauge of thehole and protect the bit body.

The positioning and orientation of inserts 14 `and 11 to cause theformation of shoulder S has been found to result in a substantialdecrease in the vertical force which must be exerted by inserts 14 tocut away the peripheral portion of the hole. As previously discussed,the inserts in a percussion bit which cut and remove that portion of thebore hole bottom nearest the side wall are subject to the greatestabrasive forces and stresses, but I have found that if the inserts arearranged in the manner shown kto form the shoulder-like protrusion Sbeneath the outermost inserts 14, the Vertical force which must beexerted by these latter inserts is substantially reduced.

T-his reduction in force arises from the fact that the material formingshoulder protrusion S is unconfined 4by other formation material at itsinner face, and thus may be fractured upon applying an impact force tothe top of the protrusion. When the protrusion is of the configurationshown in FIGURE 4, for example, the impact of inserts 14 upon its uppersurface will cause the shoulder to fracture approximately along orparallel to fracture plane F, and the protrusion will break oli inrelatively large pieces of material. The force which insert 14 mustexert on the protrusion to fracture it is, moreover, substantially lessthan that which would be required for an insert, located at the samedistance fromthe longitudinal axis of Athe bit body 1 as insert 14, tocut or chip materialfrom the bottom surface of a non-shouldered hole,and, further, the volume of the piece of material formed by fracturingshoulder S is substantially larger. Thus, by arranging inserts 11 toform protrusion S in the formation, the vertical force which must beexerted by inserts 14 is substantially reduced and a larger chipresults, diminishing the wear on inserts 14 and the danger of theirbreaking or failing prematurely. It may be considered that inserts 11 ineffect prepare the portion of the formation upon which inserts 14 mustact by reducing the force necessary to remove it.

A feature of importance lto the successful performance of my inventionis the downward and outward inclination of inserts 11 with theirlongitudinal axes at small, acute angles with the longitudinal axis ofthe bit. The nature of tungsten carbide and other hard, wear-resistantmaterials used for bit inserts in such that while they have greatcompressive strength they are relatively 4brittle and weak in tension,and thus will crack, break, or

otherwise fail under the influence of a substantial lateral (or bending)force. It will be evident from FIGURE 4 that if insert 11 were alignedwith its longitudinal axis parallel to the longitudinal axis of the bit,the upstanding side of protrusion S wouldL exert a substantial lateralforce on insert 11 as the bit is driven downwardly. Similarly, if insert11 were inclined at too great an angle to the vertical (e.g., at greaterthan about 45 degrees), the resistance of the material forming thebottom of the bore hole would impart an excessive lateral force to theinsert. Therefore, it is important that the longitudinal axis of insert11 be inclined so that the resultant of the vertical and horizontalforces acting on the insert at impact is more nearly parallel to theinserts longitudinal axis, reducing the tensile or bending forces on theinsert and causing it to be subjected almost entirely to compression.Other advantages resulting from such an orientation are t-hat theinserts 11 are surrounded by a substantial amount of body metal on allsides, reducing the possibility of their being torn or cracked out oftheir sockets and that surface 13 may be tapered to allow the iiushingiiuid to freely pass the inserts. While the angle of inclination ofinsert 11 will vary depending on the size of the bit, impact force, andmany other factors, I have found that satisfactory results are obtainedif this angle is set at about 25 degrees.

Upon impact, insert 14 is likewise subjected to both vertical andhorizontal forces, but in this case these forces are necessaril greaterthan those acting on insert 11. The body metal surrounding insertslocated in the position of insert 14, i.e., in a position to act bothupon the side wall and bottom of the hole, is particularly subject tocracking and wear, and it is desirable to so orient these inserts thatas much body metal as possible surrounds them. However, in bits which donot form protrusion S in the formation, if the insert 14 is oriented toresist in compression the larger vertical force normally exerted by thebottom of the hole, the desirable amount of surrounding body metalcannot generally be used, and, conversely, if the insert is oriented toallow a large amount of body metal on all sides, it is subjected toexcessive lateral forces in a vertical direction.

By contrast, the formation of protrusion S caused by the operation ofthe bit of this invention reduces the vertical reactive forces receivedby insert 14. Consequently, the resultant of the vertical and horizontalreactive forces on insert 14 is both diminished and acts along a line ata greater acute angle to the longitudinal axis of the bit, allowinginsert 14 itself to be oriented at an angle approaching this greaterangle and thus to be surrounded by a greater amount of body metal. Whilethe angle of inclination of insert 14 will also vary depending uponseveral factors, it has been found that in most cases the angle ofinclination of inserts 14 shouid be at least as large as that of inserts11. Gauge-holding inserts 14 may be of greater diameter than the innerinserts for greater resistance to lateral forces.

Another factor to be considered is the shelf angle A, which may bedefined as the angle which a line T, drawn at a tangent to the free endsof inserts 14 and 11 (both rotated into the same plane), makes with aline perpendicular to the longitudinal axis of the bit. The shelf angle,which is of course partially dependent upon the angles of inclination ofinserts 14 and 11, is so chosen that protrusion S will fracture underthe impact of insert 14 while preventing an excessive lateral load oninsert 11. If this angle is too great, protrusion S will not break off.For drilling in friable materials such as granite or hard limestone, ithas been found that a shelf angle on the order of 35 degrees is satisfactory.

The depth D of the shelf is selected to be several times the depth of asingle chip made by the impact of a vertically oriented insert (such asinserts As a practical matter, the minimum depth for economicaloperation should be about 1A; inch, which, when protrusion S fractures,yields a chip of considerably greater volume than those formed by theother inserts in the bottom surface 5. The radial distance between thefree ends of inserts 14 and 11 depends on the depth D and shelf angle A,and is limited only in that if it is too great, insert 14 will merelychip the upper surface of shelf S rather than fracturing it.

It will be noted that inserts 9 adjacent cavity 6 are also inclined tomore nearly cause the resultant of the vertical and lateral impactforces thereon to act along their longitudinal axes. However, since theforces on these inserts are not as great as those on the outermostinserts 14, it is generally unnecessary to employ a shelf-forming row ofinserts in conjunction with them.

After protrusion S has fractured and the chip formed thereby has brokenolf, continued drilling will cause a new peripheral protrusion to form,which shelf will in turn be fractured by the impact of inserts 11 and14, and so on. As the vertical force necessary to fracture these shelvesis than that which would be required to cut directly upon the formationat the bottom of the hole, it is apparent that the outermost inserts 14of the bit are subject to less strain and wear than those ofconventional bits, and the danger of their breaking or failing issubstantially reduced.

As used in the appended claims, the terms cut and cutting are used in abroad sense, and include the chipping action customarily associated withthe percussive impact of a wear-resistant insert upon the material beingdrilled. The terms fracture and fracturing are used to denote thebreaking of the drilled material along a substantially weak plane. Thus,as has been described above, the protrusion S fractures substantiallyalong the line F.

While but one embodiment of the invention has been described herein, itwill be understood that this embodiment is illustrative only, and thatthe invention may be modified in various respects as will occur to thoseskilled in the art and the exclusive use of all modifications as comewithin the scope of the appended claims is contemplated.

I claim:

1. A percussion bit comprising a body having a transverse bottom surfaceand a side surface, first cutting inserts protruding from said bottomsurface and spaced inwardly from said side surface, and second cuttinginserts projecting from said body in the general area of intersection ofsaid bottom and side surfaces, the extremities of said second insertsextending radially beyond said side surface for maintaining the gauge ofthe hole being drilled and being spaced substantially upwardly andoutwardly from the cutting extremities of said first inserts, therebeing a substantial annular space between said first and second insertsfree of cutting elements for leaving a shoulder-like intrusion ofmaterial at the periphery of the hole bottom to facilitate chipping ofsaid periphery by said inserts.

2. A percussion bit as described in claim 1 in which said second insertsare disposed with their axes inclined at an acute angle to thelongitudinal axis of said body and are located wholly above a plane notsubstantially below said bottom surface.

3. A percussion drill bit comprising a body having a transverse bottomsurface, a generally cylindrical side surface, a radially sequentialpair of chamfers of outwardly increasing inclination at the intersectionof said surfaces, first cutting inserts protruding downwardly from saidbottom surface and spaced inwardly from said side surface, secondcutting inserts protruding from the inner of said chamfers at an acuteangle to the longitudinal axis of said body, and third insertsprotruding from the outer of said chamfers at an acute angle to saidsecond inserts and with their extremities spaced above and outwardly ofthe extremities of said second inserts and terminating at least incircumferential alignment with said side surface for maintaining thegauge of the hole being drilled, the annular space between said secondand third inserts being free of cutters so as to form a shoulder-likeprotrusion at the periphery of the hole bottom to facilitate chippingaway of said periphery by said inclined second and third cutter inserts.

4. A percussion drill bit comprising a side surface and a transversebottom surface having an elevated central portion forming a pocket,first cutting inserts protruding from said bottom surface includinginner and outer annular rows, the inserts of said inner row projectingat an inward acute angle to the longitudinal axis of said body and intosaid pocket for chipping the core formed in said pocket, said outer rowbeing wholly spaced inwardly of said side surface, and a third annularrow of cutting inserts projecting from the region of intersection ofsaid bottom and outer surfaces outwardly at an acute angle to said bodyaxis beyond said body side wall and positioned wholly upwardly from theplane of the extremities of said second row of inserts, the cutter freespacing of s aid second and third rows of inserts causing the formationof a shoulder-like protrusion of formation material at the intersectionof the side and bottom walls of the hole to facilitate cutting of theperiphery of said bottom wall by said third row of inserts.

5. A percussion bit as described in claim 4 including additionaldownwardly-protruding cutting inserts in the elevated part of saidbottom wall and between said rst and second rows of inserts.

References Cited UNITED STATES PATENTS 2,689,109 9/1954 Curtis 175--4102,774,571 12/1956 Morlan 175-410 X 2,990,025 6/1961 Talbert et al175-410 X 3,185,228 5/1965 Kelly 175--415 X 3,269,469 8/1966 Kelly175415 X 3,269,470 S/1966 Kelly 175-415 X 20 ERNEST R. PURSER, PrimaryExaminer.

1. A PERCUSSION BIT COMPRISING A BODY HAVING A TRANSVERSE BOTTOM SURFACEAND A SIDE SURFACE, FIRST CUTTING INSERTS PROTRUDING FROM SAID BOTTOMSURFACE AND SPACED INWARDLY FROM SAID SIDE SURFACE, AND SECOND CUTTINGINSERTS PROJECTING FROM SAID BODY IN THE GENERAL AREA OF INTERSECTION OFSAID BOTTOM AND SIDE SURFACES, THE EXTREMITIES OF SAID SECOND INSERTSEXTENDING RADIALLY BEYOND SAID SIDE SURFACE FOR MAINTAINING THE GAUGE OFTHE HOLE BEING DRILLED AND BEING SPACED SUBSTANTIALLY UPWARDLY ANDOUTWARDLY FROM THE CUTTING EXTREMITIES OF SAID FIRST INSERTS, THEREBEING A SUBSTANTIAL ANNULAR SPACE BETWEEN SAID FIRST AND SECOND INSERTSFREE OF CUTTING ELEMENTS FOR LEAVING A SHOULDER-LIKE INTRUSION OFMATERIAL AT THE PERIPHERY OF THE HOLE BOTTOM OF FACILITATE CHIPPING OFSAID PERIPHERY BY SAID INSERTS.